The present invention relates to plow blades mounted on the front of vehicles and, more particularly, to a method and apparatus for detachably mounting a plow blade to the front of a vehicle. Specifically, the invention is concerned with a mechanical latching arrangement of a plow blade to a vehicle through hydraulic actuation.
At present, the most commonly used arrangement for attaching a plow blade to a vehicle involves pivotally connecting an A-frame which supports the blade to a frame extension below the front of the vehicle. Vertical displacement of the blade and A-frame is provided by a hydraulic cylinder, lift arm and chain arrangement mounted above the vehicle frame. When the hydraulic cylinder is extended, the lift arm is elevated and the chain lifts the blade from the roadway. To attach the blade to the vehicle, the A-frame must be aligned with the frame extension below the front of the vehicle. This alignment comprises both lateral and vertical alignment and is time consuming and most often accomplished only with considerable manual effort, such as physically lifting and moving the plow blade. The chain is then connected from the A-frame to the lift arm. Once the A-frame and frame extension have been aligned, locking pins connect the A-frame and allow for pivotal movement of the A-frame and thus the blade relative to the vehicle.
Vehicles used for operating plow blades are generally intended to be multi-purpose vehicles. Thus, it is imperative in such cases that the plow blade be detachable for use of the vehicle without the plow. Obviously, the time and manual effort involved in connecting and disconnecting a plow blade to a vehicle is increased by the presence of inclement weather conditions, such as snow and ice, as is the safety and comfort of a person or persons doing the work. For these reasons, it is desirable to minimize the manual effort and time required to attach and/or detach the blade from the vehicle, as well as the exposure of an individual to inclement conditions while doing so.
Many efforts have been made heretofore to improve the detachability of plow blades, including the use of mechanically actuated latching devices for attaching a blade to a vehicle. In connection with such arrangements, the vehicle is moved towards the blade such that corresponding mating members on the vehicle frame and the plow blade releasably latch when proper alignment of the blade and vehicle has been obtained. Alignment of the vehicle relative to the plow blade unit poses significant problems in many of these devices since the mechanical latching devices are relatively small. When it is desired to remove the blade from the vehicle, an operator must physically disengage the latching mechanism while the vehicle and plow are being separated. Examples of these arrangements are shown in U.S. Pat. Nos. 3,285,625; 3,410,008; 3,851,894; and, 3,987,562.
Another approach at providing a detachable vehicle mounted blade involves use of a hydraulic blade lift unit which is mounted on, and detachable with, a blade assembly. Attachment of the blade assembly to the vehicle is accomplished by moving the vehicle into alignment with the plow blade assembly and then connecting the hydraulic lift unit on the blade assembly to the vehicle hydraulic system. The vehicle is then moved into contact with the plow blade assembly, assuming lateral alignment has been obtained, and the blade assembly is lifted onto the vehicle by actuating the hydraulic lift unit. Examples of systems employing such an arrangement are shown in U.S. Pat. Nos. 3,432,949 and 3,483,641. These arrangements merely provide for lifting the blade assembly onto the vehicle, and additional operations are necessary to assure locking of the blade assembly to the vehicle, such as hand actuation of mechanical linkage or bolts.
Various arrangements of hydraulic clamping mechanisms have also been utilized to latch a blade to a vehicle. One such arrangement includes relatively displaceable interengaging clamping components and a piston-cylinder unit in which the piston is extended to cause interengagement therebetween and to hold the components in interengagement. Examples of this type of mechanism are shown in U.S. Pat. Nos. 3,876,092; 4,013,182; and, 4,068,959. These devices present operational difficulties in the event that hydraulic pressure is lost. In this respect, loss of pressure causes the piston to retract and thus the holding force to be released. In another example, the piston-cylinder operation is reversed such that retraction of the piston causes the latching of a blade unit to the vehicle. This type of system is examplified by devices disclosed in U.S. Pat. Nos. 3,528,685 and 3,760,883. Neither of these devices are suitable for plow blades in that the jolting forces exerted on the blade unit can cause disengagement of the latching mechanisms. In this respect, sudden upward movement of the blade unit can overcome a spring biased clamping arrangement in one instance, and abrupt abutment of the blade unit with a stationary object can cause shearing of locking pins in the other instance.